Bartonella henselae is the etiologic agent of cat scratch disease (CSD) (Bass et al., 1997; Branley et al., 1996; Chomel, 2000) and can also cause bacillary angiomatosis (BA) in immunocompromised patients (Arvand et al., 1998; Asharaf and Letha, 2002; Birtles et al., 1991; Chomel, 1996). CSD is common in children and young adults who have had scratches or bites from infected domestic cats (Chomel, 2000) and is characterized by fever and regional lymphadenopathy. Normally, the disease self-resolves in about three (3) months. However, in immuno-compromised patients, Bartonella infection frequently manifests as a more severe and life-threatening illnesses, including BA, endocarditis, encephalopathy, and pulmonary disease (Margileth and Baehren, 1998; Regnery and Tappero, 1995). BA is characterized by cutaneous and subcutaneous vascular lesions in which the bacteria invade endothelial cells resulting in hemangiomas. BA was initially described in patients infected with human immunodeficiency virus and has been extended to include patients with proliferative vascular lesions affecting different organs such as bone, liver, and spleen (Regnery and Tappero, 1995).
Bartonella henselae is identified by molecular and serology detection (Eskow et al., 2001). Molecular identification of bacterial genes by PCR amplification is applicable only in a laboratory with the proper equipment, expertise, and quality control procedures. PCR is useful in detecting during early-stage infection where the bacterium is still present in the peripheral blood stream. Molecular detection by PCR is suggested for surgically excised infected heart valves, but is less sensitive for peripheral blood samples because of a low pathogen bioavailability.
Serology is currently the most common diagnostic test for the determination of Bartonella infection (Houpikian and Raoult, 2002, 2003; Sander et al., 2001). Bacterial isolation of this fastidious organism by culturing is difficult because of lengthy incubation periods resulting in low sensitivity, especially for patients receiving antibiotic therapy (Agan and Dolan, 2002; La Scola and Raoult, 1999).
Immunofluorescent assay (IFA) is the most common serologic test for the detection of Bartonella henselae exposure. It is a highly subjective test, and therefore prone to erroneous interpretation by those who perform the tests. Discrepant sensitivities observed in different laboratories often led to variations in the serologic result interpretation (Amerein et al., 1996; Bergmans et al., 1997; Fournier et al., 2002).
The development of a sensitive and specific assay for the detection of Bartonella henselae has been greatly hampered by the lack of information relating to the characterization of antigens of Bartonella henselae. U.S. Pat. No. 5,736,347 describes the identification of a 17-kDa protein (Anderson et al., 1995; Sweger et al., 2000) which represents one of the few characterized antigens in Bartonella henselae believed to induce antibody responses in humans. However, the '347 patent fails to provide sensitivity and specificity of the full-length 17-kDa protein. Only PCR-dot-blot hybridization and IFA detection assays were performed, hence lacking the necessary affirmation that 17-kDa protein could be a good detection antigen in an ELISA assay, particularly for IgM. Thus, whether the 17-kDa protein serves as antigen to detect an IgM response is far from clear, much less the domain(s) on the 17-kDa protein that is/are responsible for the immunogenic response.
Accordingly, there is a continuing need for an improved assay and a method for the detection of Bartonella henselae. The present invention cures the deficiency of the prior art and provides an unexpected finding that a single domain on the C-terminus of the 17-kDa protein, spanning ˜10 amino acids in length, is necessary for the binding of antibodies present in IFA-sero positive sera obtained from patients infected with Bartonella henselae. 